Multi state magnetic bubble domain cell for random access memories

Abstract

A multi-state memory cell which uses magnetic bubble domains in uniaxial material is described. The cell includes a channel in which a number of stable bubble positions separated by barriers is formed and on which select conductors are positioned to switch a bubble from one stable position to another on a threshold basis by means of coincident currents. A cell in accordance with this invention may take the form of a four-state-two conductor cell, two-bistable-state two-conductor cell, multi-state six conductor cell and six-state three-conductor cell and include destructive or non-destructive readout.

We claim: 
     
       1. A multi-state bubble memory cell comprising: channel means formed in a magnetic bubble supporting material said channel means having a number of discrete energy minima positions separated by barriers to provide stable magnetic bubble positions; and   switching means for each pair of adjacent stable positions having first select current conductor means positioned over the barrier between the two stable positions and second select current conductor means positioned adjacent to the two stable positions, for conducting predetermined coincident currents to produce a magnetic field in the cell for switching a magnetic bubble across the barrier from the one stable position to the other stable position.   
     
     
       2. A multi-state bubble memory cell as claimed in claim 1 which further includes means for sensing the presence of bubbles at the stable positions within the cell to determine the state of said cell. 
     
     
       3. A mult-state bubble memory cell as claimed in claim 1, wherein said channel has two stable bubble positions and further includes an unstable bubble position adjacent one of said stable bubble positions and sensing means located at said unstable bubble position to detect the movement of a magnetic bubble into said unstable bubble position. 
     
     
       4. A multi-state bubble memory cell as claimed in claim 1, wherein said channel has three successive stable bubble positions and further includes an unstable bubble position adjacent the first and the third stable bubble positions, and sensing means located at each of said unstable bubble positions to detect the movement of a magnetic bubble into the unstable bubble position. 
     
     
       5. A multi-state bubble memory cell as claimed in claim 1, which further includes a thin film soft magnetic material pattern positioned on said bubble supporting material to be magnetized by currents in the conductor means to enhance switching of a bubble from one position to another position. 
     
     
       6. A multi-state bubble memory cell as claimed in claim 5, wherein said thin film pattern consists of bars having poles located over the barriers between adjacent stable positions. 
     
     
       7. A multi-state bubble memory cell as claimed in claim 5, wherein said thin film pattern consists of bars having poles located over the stable bubble positions. 
     
     
       8. A multi-state bubble memory cell comprising channels means formed in a magnetic bubble supporting material, said channel means having a number 2m of discrete energy minima positions separated by barriers to provide 2m stable magnetic bubble positions, said stable bubble positions being symmetrically located along a circular path; and switching means having m select current conductor means, each of said conductor means positioned on a different axis diametrically across said channel means over two barriers between two pairs of adjacent stable positions, wherein a magnetic bubble is switched across a barrier between two adjacent stable positions when predetermined coincident currents are driven through two of the select current conductor means.   
     
     
       9. A multi-state bubble memory cell as claimed in claim 8 which further includes bubble sensing means for detecting the presence of a bubble at the stable positions within the cell to determine the state of said cell. 
     
     
       10. A multi-state bubble memory cell as claimed in claim 8 which further includes m thin film soft magnetic material bars forming a pattern on said bubble supporting material to be magnetized by the coincident currents to enhance switching of a bubble from one position to an adjacent position, each of said bars being located on a different one of said axis. 
     
     
       11. A multi-state bubble memory cell as claimed in claim 8 which further includes m thin film soft magnetic bars forming a pattern on said bubble supporting material to be magnetized by the coincident currents to enhance switching of a bubble from one position to another position, each of said bars extending across a different pair of diametrically opposite stable positions and having one pole located over each stable position. 
     
     
       12. A multi-state bubble memory cell comprising: first and second parallel channel means formed in magnetic bubble supporting material, each of said channel means having a number m of successive discrete energy minima positions separated by barriers to provide m stable magnetic bubble positions; and   switching means having (m-b) first select current conductor means, each of said conductor means successively positioned across the first and second channel means over a barrier between an adjacent pair of stable positions in each channel means and second select current conductor means positioned between the first and the second channel means, wherein a magnetic bubble is switched across a barrier between two adjacent stable positions when predetermined coincident currents are driven through one of said first conductor means and said second conductor means.   
     
     
       13. A multi-state bubble memory cell as claimed in claim 12 which further includes a thin film soft magnetic material bar located between said bubble supporting material and each of said first conductor means to be magnetized by the current in the second conductor means to enhance switching of a bubble from one position to an adjacent position in one of the channel means. 
     
     
       14. A multi-state bubble memory cell as claimed in claim 13 which further includes bubble sensing means for detecting the presence of a bubble at the stable positions within the cell to determine the state of said cell. 
     
     
       15. A multi-state bubble memory cell as claimed in claim 13 wherein m = 3 and which further includes bubble sensing means located at the third stable position of each of the first and second channel means to detect the movement of a magnetic bubble into said third stable positions. 
     
     
       16. A multi-state bubble memory cell comprising: a matrix of channels means formed in a bubble supporting material having stable magnetic bubble positions separated by barriers between adjacent stable positions located in said channel means to provide (n+1) rows and (p+1) columns of discrete energy minima positions, where n may be equal to p; and   switching means having n first select current conductor means, each of said first conductor means positioned over the barriers between the successive rows of energy minima positions and p second select current conductor means; each of said second conductor means positioned over the barrier between the successive columns of energy minima positions, wherein a magnetic bubble is switched across a barrier between two adjacent stable positions when predetermined coincident currents are driven through one of said first conductor means and one of said second conductor means.   
     
     
       17. A multi-state bubble memory cell as claimed in claim 16 which further includes a thin film soft magnetic material pattern positioned on the bubble supporting material at the conductor means crossings to be magnetized by the currents in the conductor means to enhance switching of a magnetic bubble from one position to an adjacent position.